This invention relates to a novel jack-up platform apparatus. More specifically, the subject invention relates to an offshore jack-up platform apparatus of the type utilized by the petroleum industry.
In the past, offshore platforms or towers have been extensively utilized around and upon the continental shelf regions of the world. Examples of offshore platform facilities include supports for radar stations, light beacons, scientific and exploration laboratories, chemical plants, power generating plants, mining stations, etc. Principally, however, offshore platforms have been utilized by the oil and gas industry in connection with drilling, production and/or distribution operations.
In conducting such offshore activity, several platform designs have been employed by the industry. In deep water applications, semi-submersibles or drillships, which are dynamically positioned and/or turret moored over a well site, have been effectively employed. Although semi-submersibles and drillships are highly mobile and widely utilized in deep water applications, the initial cost and subsequent operating expense reduces the desirability of such units for use in shallow water or intermediate depth applications.
In shallow water applications, fixed length towers or platforms have been extensively utilized. In this regard such platforms are fabricated on shore and transported in a generally horizontal posture to an offshore site upon a barge or buoyancy chambers within the platform legs. On site, the platform is pivoted into an upright posture and the base is positioned into firm engagement with the seabed. A platform deck is then fabricated upon the erected tower for conducting offshore operations. Such fixed platforms, although economical, require considerable time to assemble and once in position are difficult to relocate.
One platform design which combines many of the advantages of floating and fixed equipment is known as a "jack-up platform". In this connection a jack-up platform typically comprises a barge or self propelled deck operable to function in a conventional flotation capacity during transportation and in a working deck capacity on location. The deck is fitted with one or more legs which are operable to be vertically extended downward from the deck and into supporting engagement with the seabed.
In operation a jack-up platform is either towed or navigated to a desired offshore site with the jack-up legs extending through well fashioned through the deck. On site the legs are jacked downward into firm engagement with the water bed. Further jacking serves to raise the hull/deck with respect to the surface of the body of water. Once the lowermost portion of the deck is elevated above a statistical storm wave height, jacking is discontinued and drilling and/or production operations are begun from the elevated deck. Upon completion of the desired offshore operations, the deck is jacked down to the surface of the body of water and the legs are jacked up. The platform is then towed or navigated to another working station and the process is repeated. Because of its mobility and versatility, jack-up platforms have emerged as one of the most desirable forms of platform design in the industry.
The subject invention is specifically directed to a new jack-up method and apparatus operable for effecting relative vertical motion between a leg chord and a deck or hull of a jack-up platform.
In the past, various designs have been at least theorized to jack supporting legs with respect to a deck of a jack-up platform. One such design comprises a rack and pinion assembly wherein a rack is welded along the length of each platform leg. Pinion gears are then either hydraulically or electrically driven from assemblies mounted upon the platform deck to raise and lower the legs. Another design utilizes pneumatic collars which operably surround and selectively engage the platform legs. Jack units cooperate with the pneumatic collars to effect vertical relative movement of the legs with respect to the deck.
One of the most popular designs comprises various modifications of a hydraulic piston and cylinder arrangement operable to act between a platform deck and adjacent supporting legs. Initial hydraulic designs, however, tended to be heavy, bulky structures requiring a number of closely fitting parts and guide members between the platform legs and the jacking assemblies. These members were subject to misalignment and jamming tendencies during operation. In addition to structural complexities and inefficiencies, early hydraulic designs often fixedly mounted one end of the hydraulic lifting assemblies to a deck frame. This design thus required the unit to work under load in both directions and tended to limit the jack capacity during the stroke which included the piston rod.
One system which has achieved a considerable degree of commercial success is disclosed in a United States Richardson U.S. Pat. No. 3,412,981 of common assignment with the instant application. In accordance with the Richardson invention, first and second yokes are mounted about a platform leg chord and are spaced by hydraulic jack cylinders mounted at the ends of the yoke legs. The yoke and hydraulic jacking assemblies float within a jack housing mounted upon the deck and function as more specifically disclosed in the patent specification to raise and lower the leg chord with respect to the jack housing and deck.
Although this previously known Richardson structure has achieved a significant degree of acceptance, it would be desirable to provide a jack-up method and apparatus wherein the size and weight of the jack-up apparatus may be reduced. In this regard, the jack housing and yoke must be sized to carry reaction moments during a jacking operation and thus represent a considerable weight factor relative to the overall platform design. Additionally, it would be desirable to provide a jack-up apparatus wherein the jacking assemblies would admit to prepackage fabrication and testing techniques and convenient final installation and assembly. In a similar vein, it would be highly desirable to provide a jack-up apparatus which would be operably releasable from a platform deck such that individual units might be interchangable or removable as needed or desired. Yet further it would be desirable to provide a novel jack-up method and apparatus wherein reaction moments created between an off-shore platform leg chord and pin assemblies extending between the leg chord and the jacking apparatus might be efficiently reacted.
The difficulties and/or limitations suggested in the preceding are not intended to be exhaustive, but rather are among many which may tend to reduce the effectiveness of prior jack-up methods and apparatus. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that methods and apparatus appearing in the past for raising and lowering leg chords on jack-up platforms will admit to worthwhile improvement.